This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Measurement of cortisol in hair is emerging as a biomarker for chronic stress in human and nonhuman primates. Because of its external nature, hair is potentially vulnerable to a loss of cortisol from within the hair shaft due to repeated exposure to various substances such as shampoo (in humans) and water (in free-ranging monkeys). This study examined the influence of both factors on the hair cortisol levels of indoor laboratory housed rhesus monkeys. The effect of shampoo and water cannot be tested in humans because of the need to have hair that had no prior exposure to these elements. Hair was shampooed and exposed to water in vitro (i.e., after it had been gently shaved from the nape of the neck of the rhesus monkeys).